{"id":5301,"date":"2025-05-26T14:29:48","date_gmt":"2025-05-26T13:29:48","guid":{"rendered":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/?page_id=5301"},"modified":"2025-07-15T17:48:03","modified_gmt":"2025-07-15T16:48:03","slug":"ip-addressing-scheme","status":"publish","type":"page","link":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/?page_id=5301","title":{"rendered":"IP Addressing Scheme"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">IPv4<\/h2>\n\n\n\n<p><a href=\"https:\/\/datatracker.ietf.org\/doc\/html\/rfc1918\" target=\"_blank\" rel=\"noreferrer noopener\">RFC1918<\/a> reserves three sets of IPv4 address space for &#8220;private internets&#8221;:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>10.0.0.0 &#8211; 10.255.255.255 (10\/8 prefix)<\/li>\n\n\n\n<li>172.16.0.0 &#8211; 172.31.255.255 (172.16\/12 prefix)<\/li>\n\n\n\n<li>192.168.0.0 &#8211; 192.168.255.255 (192.168\/16 prefix)<\/li>\n<\/ul>\n\n\n\n<p>Of these, the 10.0.0.0 range is often used by large organisations for their internal network and the 192.168.0.0 range is often used by domestic and small-business installations (and devices like mobile broadband adaptors), whereas the 172.16.0.0 range seems neglected by comparison &#8211; which makes it a good one to choose, to reduce the risk of address-space contention.<\/p>\n\n\n\n<p>That leaves the question of how to slice up the 172.16.0.0\/12 address space. Some considerations:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>I&#8217;ve always felt a \/24 network, accommodating up to 254 hosts, is a bit &#8216;small&#8217; so it&#8217;s best to use larger subnets; might as well standardise on a \/22 which can accommodate up to 1023 hosts\n<ul class=\"wp-block-list\">\n<li>Might there be a risk of needing more hosts per subnet? Seems unlikely, given the use of multiple VLANs \/ subnets, but probably wise to make provision for each \/22 to change to a \/21 (2047 hosts) instead (but initially operate it as a \/22; effectively means leaving another \/22 unused, next to it)<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>There will be multiple &#8216;buildings&#8217; or &#8216;sites&#8217; which need to share the address space\n<ul class=\"wp-block-list\">\n<li>At least two (the House and the Outbuildings); maybe treat &#8216;remote (VPN) users&#8217; as a third &#8216;building&#8217;? So provision for at least four &#8216;sites&#8217;<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>There will be multiple VLANs \/ subnets at each &#8216;site&#8217; so need to leave provision for enough of those\n<ul class=\"wp-block-list\">\n<li>64 VLANs should be enough, though allowing for 128 wouldn&#8217;t hurt<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p>That leads to a couple of options:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>4 &#8216;sites&#8217;, each with 128 x \/21 VLANs (or 256 \/22 VLANs)<\/li>\n\n\n\n<li>8 &#8216;sites&#8217;, each with 64 x \/21 VLANs (or 128 \/22 VLANs)<\/li>\n<\/ul>\n\n\n\n<p>I settled on the second of those:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>172.16.0.0\/15 (i.e. 172.16.0.0 &#8211; 172.17.255.255) reserved for networks in the House\n<ul class=\"wp-block-list\">\n<li>172.16.0.0\/21 (i.e. 172.16.0.0 &#8211; 172.16.7.255) reserved for future use<\/li>\n\n\n\n<li>172.16.8.0\/21 (i.e. 172.16.8.0 &#8211; 172.16.15.255) reserved for VLAN 8 &#8211; initially provisioned as a \/22<\/li>\n\n\n\n<li>172.16.16.0\/21 (i.e. 172.16.16.0 &#8211; 172.16.23.255) reserved for VLAN 16 &#8211; initially provisioned as a \/22<\/li>\n\n\n\n<li>&#8230;<\/li>\n\n\n\n<li>172.17.248.0\/21 (i.e. 172.17.248.0 &#8211; 172.17.255.255) reserved for VLAN 504 &#8211; initially provisioned as a \/22<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>172.18.0.0\/15 (i.e. 172.18.0.0 &#8211; 172.19.255.255) reserved for networks in the Outbuildings\n<ul class=\"wp-block-list\">\n<li>172.18.0.0\/21 (i.e. 172.18.0.0 &#8211; 172.18.7.255) reserved for future use<\/li>\n\n\n\n<li>172.18.8.0\/21 (i.e. 172.18.8.0 &#8211; 172.18.15.255) reserved for VLAN 8 &#8211; provisioned as a \/22<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>172.20.0.0\/14 (i.e. 172.20.0.0 &#8211; 172.23.255.255) reserved for future use<\/li>\n\n\n\n<li>172.30.0.0\/15 (i.e. 172.30.0.0 &#8211; 172.31.255.255) reserved for &#8216;remote&#8217; networks\n<ul class=\"wp-block-list\">\n<li>172.31.248.0\/21 (i.e. 172.31.248.0 &#8211; 172.31.255.255) reserved for WireGuard VPN users<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>IPv4 RFC1918 reserves three sets of IPv4 address space for &#8220;private internets&#8221;: Of these, the 10.0.0.0 range is often used by large organisations for their internal network and the 192.168.0.0 range is often used by domestic and small-business installations (and &hellip; <a href=\"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/?page_id=5301\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"parent":5823,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-5301","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/5301","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5301"}],"version-history":[{"count":8,"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/5301\/revisions"}],"predecessor-version":[{"id":5876,"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/5301\/revisions\/5876"}],"up":[{"embeddable":true,"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=\/wp\/v2\/pages\/5823"}],"wp:attachment":[{"href":"https:\/\/www.marshflattsfarm.org.uk\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5301"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}